Change tire size effects?

u wont notice a difference.... not to mention that modern cars r made to adjust for a 3prct difference in tire size......and if ur tires r worn..wich they probably r since ur changing them the new "smaller" tire may actually b bigger than the old tires

Personally, I don't think it is even enough of a difference to be correctable.. Even if it is a digital speedo, I dont think it will change.. I am not a certified mechanic, just a hotrodder of many years, the speedo off for one reason or another is common, your wider stance of the 70 profile will drop it in heigth slightly, but that same slight difference gives a little less side roll while cornering..

It may ride a little rougher, You will traveling approx 3 mph faster than the speedo will show. If it is on a V/8 unit and you do not haul much weight - the mileage, (mpg) will increase but, very little. The tire grip in snow and on slick surfaces, especially when fast braking will be less, due to less PSI on the roadway, with the wider tread. Most of the above will be very slight.

this is true, but not by much difference, you calculate the new value of the height of the tire and divide it by the original height of the tire to figure out your proportional difference in speed, in fuel economy you might lose 5%-10% of it

You are right.

it won't be noticeable